1. Field of the Invention
The present invention relates to an optical apparatus for reading an image or forming an image to be employed in an image scanner, LED printer and so forth.
2. Description of the Related Art
As an optical apparatus for reading an image, there are apparatus employing a reduction optical system which forms a reduced image of an original on an image sensor, such as a CCD and so forth by means of a convex lens and apparatus employing an equal magnification optical system which forms an equal magnification image of the original on an elongated image sensor employing graded refractive type lens array, a rod lens array and so forth. Since the original surface and the image sensor are placed in close proximity to each other, the latter will also referred to as contact optical system.
When the apparatus is made compact, the contact optical system is advantageous. For example, when the contact optical system is employed in a portable image scanner, the apparatus employing contact optical system, has to be made further compact.
In the graded refractive type lens array or the rod lens array to be employed in the optical apparatus employing the contact optical system, it is difficult to set a focal distance to be in the order of several mm or less. In practice, approximately 15 to 20 mm of focal distance is required.
On the other hand, in a micro-lens array formed with a plurality of fine lens on a substrate, it is possible to produce a lens having short focal distance relatively easily by selecting production process and so forth. Also, it is possible to form an erecting equal magnification image by employing a plurality of stages of lens array. Therefore, there has been proposed to avoid parallax by projecting a display image of a liquid crystal display on a protecting glass placed in front thereof (Japanese Unexamined Patent Publication No. SHO 63-263520).
As set forth above, in order to make the optical apparatus compact, it becomes necessary to shorten an optical length. However, in case of the graded refractive type lens array or the rod lens array, it is practically impossible to shorten the optical length to be shorter than or equal to 10 mm.
Accordingly, for application to an ultra-compact card type image scanner for reading original in size of a name card size, for example, the conventional apparatus is not sufficiently compact. In addition, since the graded refractive type lens array or the rod lens array is expensive, it is not possible to realize sufficiently low price as personal use apparatus.
Also, in the conventional micro-lens array, removal of crosstalk light from adjacent lens is difficult. Furthermore, in order to enhance efficiency of use of the light, three stages or more of lens array become necessary to make the structure complicate.
Namely, as shown in FIG. 21(a), when a magnification of an intermediate image is 1 and two stages of lens arrays are employed, substantial part of light other than the central portion of the intermediate image may be directed out of the opening portion of the lower lens to cause fluctuation of brightness in the formed image. Also, crosstalk cannot be avoided. For improvement, when the third stage intermediate lens is inserted at the position of the intermediate image (see Japanese Unexamined Patent Publication No. SHO 63-263520), while the problem of fluctuation in brightness of the image can be solved, the structure becomes complicate and the problem of crosstalk from the adjacent lens is maintained unsolved.
On the other hand, it is considered to employ normal convex lens and a light shielding cylindrical body for preventing crosstalk in combination in place of the conventional rod lens. However, in such case, since it is required to absorb the light on the inner periphery of the cylindrical body, production of such cylindrical body is difficult. Therefore, such apparatus is not suitable for mass-production.